The present invention relates to printed circuit boards usable, for example, in personal computers and, in particular, to the configuration of electrical conductor pads formed on the printed circuit boards.
A conventional printed circuit board (p.c. board) 10, depicted in FIGS. 3 and 4, comprises a base 12, and a high density row of electrically conductive raised pads 14 formed preferably on each side 16 of the board, e.g., by an etching process. There may be two rows of staggered pads 14a, 14b as shown in FIG. 4, or only a single row of non-staggered pads. The pads 14a, 14b are typically gold plated and positioned to be engaged by gold plated flexible contacts 20 disposed within a slot 22 of a cardedge connector 24 (see FIGS. 1 and 2) when the board 10 is inserted into the slot.
Forward portions of the pads 14a may optionally comprise narrow traces 28 to provide smooth surfaces along which the contacts 20 can travel between the other pads 14b toward a wider rearward portion of the pad in order to prevent the gold plating from being rubbed off the contacts 20 after repeated removal and re-installation of the circuit board.
Heretofore, it has been necessary to manufacture the p.c. boards 10 and cardedge connectors 24 under very tight dimensional tolerances in order to ensure that the contacts properly engage the pads 14 once the p.c. board has been inserted into the cardedge connector. That is, if the pads 14a, 14b are not located with a high degree of precision on the base 12, or if too much relative lateral movement (i.e., rightward or leftward movement in FIG. 3) is permissible between the p.c. board and connector, the contacts, especially very thin contacts may follow a path which results in a lack of electrical contact between the contacts 20 and the pads 14a and/or 14b after the p.c. board has been installed. It has been surmised that if the dimensional tolerances are not sufficiently tight, one or more of the contacts 20 may follow a path P depicted in phantom lines in FIG. 4 wherein the contact is offset from the center axis CA of the respective pad 14a and travels laterally to the right (or left) off the pad 14a after traversing a frontal edge 32 of the pad, which edge 32 extends perpendicularly relative to the axis CA. A similar problem can occur in connection with the front edge 33 of the pads 14b.
While that problem can be avoided if sufficiently tight dimensional tolerances are maintained during manufacture of the p.c. board and cardedge connector, the need to adhere to such tight tolerances appreciably increases the manufacturing cost and effort.